The present invention is directed to a shackle with a concave shaped diameter section in the center portion of the threaded cross member between the two lugs of the shackle. This feature facilitates the automatic centering of the connection (typically, the eye of a wire or rope) loaded on the cross member of the shackle.
A shackle is comprised of a loop (referred to as the shackle body or bail)—often forged and often semi-circular in shape—with lugs located on each end. A cross member is fitted between these lugs and is typically screwed into the inside diameter of one of the lugs threaded to accept it. The cross member is also referred to as a closure pin, closure bolt or closure cross member. When using a shackle to lift a load with a crane or other hoisting device, the connection of the eye of the rope or wire on the shackle closure cross member should be at 90 degrees to the shackle closure cross member centerline. This lifting configuration provides optimum load rating for the shackle. However, this configuration is often difficult to obtain because most common shackles have a constant diameter closure cross member which allows the eye connection to the closure cross member to move along the member and naturally adjust to be at an angle less than 90 degrees to the shackle closure cross member centerline.
Currently, several stop-gap measures are used with constant diameter closure cross member shackle configurations. One such measure is to pack the closure cross member with washers on either side of the eye connection to the closure cross member. In this way, the eye of the rope or wire is centered in the middle of the closure cross member by the use of the washers on both sides of the closure cross member. Another measure calls for the use of a sleeve add-on device that fits over the closure cross member shaft. The sleeve fits between the two lugs and has a center depression which works to center the hoisting rope. The draw back with both of these stop-gap measures is that both require many different sized washers and sleeves to be available because of the many different sized shackles employed in a typical hoisting job. There is a propensity for these small type add-on parts to get lost when not in use and not be available when needed.
The prior art discloses a shackle arrangement with a bail (the loop portion of the shackle) having a lug at each end designed to accept a closure cross pin with threads on one end and a “bowed” cross pin shaft in the center portion of the bail. This configuration is described as creating a valley in which the eye of the hook or rope attached to the shackle will always ride. The difference between the prior art and the present invention is that the present invention uses the machining or casting of a conical shape in the closure cross member center portion. This results in the load on the closure cross member being in line with the centerline of the internal diameters of the lugs on the bail that support the closure cross member. The prior art provides for a “valley” resulting in the loading on the closure cross member not being in line with the centerline of the internal diameters of the lugs of the bail. The difference in loading and therefore capacity is that the prior art “valley” configuration subjects the closure cross member to additional bending loads not present with the “in line” configuration of the present invention. As such, the “valley” configuration cannot hold the same maximum load as the in-line configuration because of the additional stresses to which the valley configuration shackle is subject.
The additional difference between the prior art and the present invention is the cross-sectional area of the closure cross member. The present invention provides for a closure member with a cross-sectional area (locally reduced by the conical shaped center section) equal to the area of the larger of the two lugs attached to the loop of the shackle. The prior art configuration provides for a cross-sectional area of the cross member being less than the area of the hole of the larger of the two lugs attached to the loop of the shackle. The cross sectional area of the closure cross member is reduced because the diameter of the cross member must be less than the diameter of the hole in the larger of the two lugs to accept the cross member in its distorted configuration to create the “valley” between the two lugs when the pin is inserted between the two lugs and screwed in place.